It is known that when laser light from a laser light source irradiates the surface of a brittle material to be processed, heating distortions generated at this time due to the changes in heating and cooling can be used to process the brittle material.
For example, JP H3-13040B discloses a processing method in which the brittle material is cleaved by guiding a crack formed at the start of the processing of the brittle material along a processing line by the heat strain due to the laser light irradiation. Further, Tokuhyo H8-509947 (Japanese Patent No. 3027768) discloses a processing method in which a crack is formed from the surface of the material to a predetermined depth by the heat strain due to laser light irradiation onto the brittle material, and the brittle material is cut using this crack.
Typical laser light sources used in this type of processing include gas lasers such as HF lasers with an emission wavelength of 2.9 μm, CO lasers with an emission wavelength of 5.5 μm, and CO2 lasers with an emission wavelength of about 10 μm and the like. Furthermore, solid-state lasers such as ruby lasers or semiconductor lasers or the like, which emit a variety of wavelengths, are commercially available.
Of the laser light sources available commercially, laser light with wavelengths of about 1 to 3 μm is used for processing semiconductor wafers of silicon and the like, while laser light of wavelengths of about 5 to 10.6 μm is used in the processing of brittle materials such as glass and the like. Furthermore, various ceramic materials are processed using laser light with wavelengths of about 1 to 10.6 μm.
However, with the processing method using laser light, the light absorptance of the processing material will greatly change depending on the wavelength of the irradiated laser light. When that absorptance is large, most of the irradiated laser light is absorbed in the vicinity of the material surface, and direct heating by irradiating laser light that does not depend on thermal conduction will not extend more than a few μm from the material surface.
Showing this condition in FIG. 6, the heated region that is heated by irradiation of laser light L is extremely localized in the surface vicinity when compared to the thickness of the brittle material W, and propagation of heat to the material interior occurs by thermal conduction (thermal conduction zone). Due to this, as a large amount of time is needed before the material interior is extensively heated, this has been a large hindrance to speeding up the process time.
According to the processing methods disclosed in JP H3-13040B or Tokuhyo H8-509947 (Japanese Patent No. 3027768), consideration towards the selection of the laser light wavelength is not particularly strict, and often the irradiated laser light is not at the optimum absorption wavelength. Because of this, a long time is required to increase the temperature of the interior of the material, it is necessary to lengthen the laser light irradiating period, and processing speed cannot accelerated.
Further, as a different problem which occurs when the irradiating time is lengthened, before attaining the temperature necessary for processing (crack formation), the inside of the material, the temperature of the surface vicinity of the irradiated portion is heated to near or above the melting temperature of the material, and there is the problem that if the vicinity of the material surface melts, it becomes difficult to obtain an accurate scribe line. It should be noted that in the processing method disclosed in Tokuhyo H8-509947 (Japanese Patent No. 3027768), there is also the problem that because a long time is required to heat the material interior to a sufficient temperature, cracks cannot be formed deep into the material within the heating times for scanning speeds that are used in practice.
In order to obtain a practically effective processing speed, examples have been disclosed which are realized by the addition of contrivances onto optical systems that are combinations of various lenses or optical parts, such as a laser beam emitted from the laser emitting portion arranged so as to widen in the scanning direction in an elliptical-shape or oval-shape, with the intention to have an irradiation area of laser light used in the process that is as wide as possible.